The Difference Between GCF and LCM
Submitted by Andy_B on Wednesday, 24 February 2021 Page Views: 652
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Here we will be looking at the best methods to calculate greatest common factor (GCF).
1. Listing Method
The first step is to list out all the factors of the given numbers. The next step is to find the factor that is common to all the given numbers. The greatest factor that is common to all numbers becomes the GCF. Thus, If we find the common factors of two numbers, the greatest common factor can be produced from the list of these factors.Example: Say we have to find the GCF of 4, 16 using the listing method.
- Factors of 4 = 1,4
- Factors of 16 = 1, 2, 4, 8, 16.
- Common Factors of 4, 16 = 1, 4.
2. Prime Factorisation Method
Listing all the factors can be very time-consuming, primarily if we deal with large numbers. In such a case, it is easier to find the prime factors of the numbers to find the GCF. In this method, the first thing to do is list all the prime factors of each number. The next step is to find all the common prime factors. By multiplying these common prime factors, the resulting number is the GCF of the two numbers.Example: We have to find the GCF of 4, 16 using the prime factors method
- Prime Factors of 4 = 2 × 2
- Prime Factors of 16 = 2 × 2 × 2 × 2
- Common Prime Factors = 2 × 2
What is LCM?
The full form of LCM is Least or Lowest Common Multiple. It can be defined as the lowest common multiple that is divisible by the given set of natural numbers. The LCM has to be a multiple of all the given numbers. Thus, the LCM of the numbers is the smallest number that appears as a multiple and can be divided by the given numbers.Methods to Calculate LCM
1. Listing Method
In this method, we make a list of all the multiples belonging to the given set of numbers. The smallest multiple, which is common to all numbers, provide us with the LCM.Example: To find the LCM of 4, 16 using the listing method
- Multiples of 4: 4, 8, 12, 16, 20, 24 …..
- Multiples of 16: 16, 32, 48 ….
- LCM: 16
2. Prime Factorisation Method
To find the LCM using this method, we first write all the numbers as a product of their prime factors. We then write down all the prime factors making sure that the common factors are listed only once. By multiplying these, we get the LCM.Example: LCM of 4, 16 using the prime factors method is 16
- Prime Factors of 4 = 2 × 2
- Prime Factors of 16 = 2 × 2 × 2 × 2
- Thus, LCM = 2 × 2 × 2 × 2 = 16



